The present invention relates generally to the field of circuit breakers, and more particularly to a molded case circuit breaker with a signal accessory.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially a stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as 160 amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range.
In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. In a short circuit condition, the higher amount of current flowing through the circuit breaker activates a magnetic release which trips the breaker in a much faster time than occurs with the bi-metal heating. It is desirable to tune the magnetic trip elements so that the magnetic trip unit trips at lower short circuit currents at a lower continuous current rating and trips at a higher short circuit current at a higher continuous current rating. This matches the current tripping performance of the breaker with the typical equipment present downstream of the breaker on the load side of the circuit breaker.
In certain situations, an operator of an electrical system may desire to know if a circuit breaker is open, closed or tripped from a remote location. Such circumstances can include applications for maintenance and control. It may also be used in applications to provide synchronizing of several breakers, together with other accessories, to open and close several circuit breakers. One device used for signaling the state of a circuit breaker from a remote location is a signal accessory such as a bell switch or an auxiliary switch. Existing signal accessories currently used have several disadvantages. Some such signal accessory accessories must be installed in the circuit breaker housing behind the main cover and in close proximity to electrically live parts and connections. Other signal accessory accessories require the user to provide terminal connections to the switch wires. Further examples of present signal device accessories are designed to be used with a single circuit breaker frame, i.e., for each current rating of the circuit breaker a specially designed signal device accessory is required.
Thus, there is a need for a signal accessory to signal the state of a circuit breaker from a remote location that can be installed in the main cover of the circuit breaker without exposing the electrically live parts of the circuit breaker. There is a further need for a signal device that can be used with several circuit breaker frame sizes, that is, a single signal accessory that will operate over a wide range of constant current ratings for the circuit breaker. There is an additional need for a signal accessory with which a customer can connect its control wiring directly to the signal device without any additional rewiring. And further, there is a need for a signal device for a circuit breaker that can be installed in a circuit breaker utilizing a common latching protrusion that provides an audible snap fit installation.
The present invention is embodied in a signal accessory for a molded case circuit breaker, with the circuit breaker having an operating mechanism with a cradle pin, a cross bar and a trip bar and a breaker cover. The signal accessory comprises a signal accessory mounting having a bottom mount and a top mount coupled to the bottom mount with the top mount configured to receive a switch and engage the breaker cover in an accessory socket. A switch member is rotably mounted on the bottom mount with the switch member having an actuator lever in contact with the operating mechanism of the circuit breaker and an actuator pad in contact with a switch mounted on the top mount. When the circuit breaker is opened or closed the operating mechanism moves a cross bar which is attached to the movable contact arm. The cross bar moves the actuator lever of the switch which changes the state of the switch. Another embodiment of the present invention includes at least one additional switch mounted on the top mount and in operative contact with the actuator pad. The signal accessory mounting will accommodate a combination of auxiliary switches and an alarm switch. An operator of the signal accessory wires the auxiliary switch and the alarm switch to respective switching circuit and alarm circuit to provide remote indication of the status of the circuit breaker, i.e., open or closed, and tripped or untripped.
Another embodiment of the signal accessory comprises an integrated top and bottom mount with one switch member in operative contact with the trip bar of the circuit breaker and with another switch member in operative contact with the cross bar of the circuit breaker.
The present invention also embodies a method for signaling the state of a molded case circuit breaker having an operating mechanism configured to open and close a power circuit, a trip unit with an intermediate latch and a breaker cover, to a remote location, including the steps of installing a signaling accessory in the breaker cover with the signaling accessory having an alarm actuator in operative contact with the trip unit and a switch actuator in operative contact with the operating mechanism, wiring the signaling accessory having an alarm actuator to an alarm circuit and wiring the signaling accessory to the switch actuator in a switch circuit. In changing the state of the signaling accessory having the alarm actuator with one of either a cradle pin in the operating mechanism and a trip bar whereby the state of the circuit breaker is indicated in the alarm circuit and changing the state of the signaling accessory having the switch actuator in operative contact with a cross bar of the operating mechanism, whereby the state of the circuit breaker is indicated in the switch circuit as being either on or off. The method includes retaining the signaling accessory in the circuit breaker cover such that a snap is generated as the signaling accessory is nested in an accessory socket of the circuit breaker cover.